If $3 \times 11 \times 13 \times 21 = 2005 +b$, what is the value of $b$?
Explanation: To multiply the left-hand side quickly, we note that among the 4 numbers, we have $11 \times 13 \times 7 = 11 \times 91 = 1001$. Then, we have 9 left over, so the total product is 9009, and subtracting 2005, we get $\boxed{7004}$.